Conventional transmissive liquid crystal displays (LCDs) use a white backlight, together with patterned color filter arrays (CFAs), to create colored pixel elements as a means of displaying color. Polarizing films polarize light. The pixels in a conventional liquid crystal display are turned on or off through the use of an additional layer of liquid crystals in combination with two crossed polarizer structures on opposite sides of a layer of polarizing liquid crystals. When placed in an electrical field with a first orientation, the additional liquid crystals do not alter the light polarization. When the electrical field is changed to a second orientation, the additional liquid crystals alter the light polarization. When light from the polarizing liquid crystals is oriented at ninety degrees to the orientation of the polarizing film in a first orientation, no light passes through the display, hence, creating a dark spot. In a second orientation, the liquid crystals do rotate the light polarization; hence, light passes through the crystals and polarizing structures to create a bright spot having a color as determined by the color filter array.
This conventional design for creating a display suffers from the need to use a polarizing film to create polarized light. Approximately one half of the light is lost from the backlight; thus, reducing power efficiency. Just as significantly, imperfect polarization provided by the polarizing film reduces the contrast of the display. Moreover, the required additional use of a color filter array to provide colored light from a white light source further reduces power efficiency. If each color filter for a tri-color red, green, and blue display passes one third of the white light, then two thirds of the white light is lost. Therefore, at least 84% of the white light generated by a backlight is lost.
The use of organic light emitting diodes (OLEDs) to provide a backlight to a liquid crystal display is known. For example, U.S. Patent Application Publication No. 2002/0085143 A1, by Jeong Hyun Kim et al., published Jul. 4, 2002, titled “Liquid Crystal Display Device And Method For Fabricating The Same,” describes a liquid crystal display (LCD) device, including a first substrate and a second substrate; an organic light emitting element formed by interposing a first insulating layer on an outer surface of the first substrate; a second insulating layer and a protective layer formed in order over an entire surface of the organic light emitting element; a thin film transistor formed on the first substrate; a passivation layer formed over an entire surface of the first substrate including the thin film transistor; a pixel electrode formed on the passivation layer to be connected to the thin film transistor; a common electrode formed on the second substrate; and a liquid crystal layer formed between the first substrate and the second substrate.
A method for fabricating the LCD in U.S. Patent Application Publication No. 2002/0085143 A1 includes the steps of forming a first insulating layer on an outer surface of a first substrate; forming an organic light emitting element on the first insulating layer; forming a second insulating layer over an entire surface of the organic light emitting element; forming a protective layer on the second insulating layer; forming a thin film transistor on the first substrate; forming a passivation layer over an entire surface of the first substrate including the thin film transistor; forming a pixel electrode on the passivation layer; and forming a liquid crystal layer between the first substrate and a second substrate. However, this prior art design does not disclose a means to increase the efficiency of the LCD.
U.S. Pat. Nos. 6,485,884 issued Nov. 26, 2002 to Martin B. Wolk et al., titled “Method For Patterning Oriented Materials For Organic Electronic Displays And Devices” discloses the use of patterned polarized light emitters as a means to improve the efficiency of a display. The method includes selective thermal transfer of an oriented, electronically active, or emissive material from a thermal donor sheet to a receptor. The method can be used to make organic electroluminescent devices and displays that emit polarized light. There remains a problem, however, in that there continues to exist incomplete orientation of the electronically active or emissive material from a thermal donor sheet to a receptor. Hence, the polarization of the emitted light is not strictly linearly polarized, therefore, the light is incompletely polarized.
There is a need, therefore, for an alternative backlight and a novel display design that improves the efficiency of polarized light production, thus and thereby improving the overall efficiency of a liquid crystal display that incorporates the alternative backlight.